Reinforced foil susceptor adhesive structure

ABSTRACT

Reinforced foil susceptor structures are disclosed. These structures are thin, allowing them to heat quickly when used in an induction heating process, but are also easy to handle and sturdy. The susceptor structures may comprise two foil layers (e.g., aluminum having a thickness of no greater than 2 mils) sandwiching between them a reinforcing layer (e.g., made from a thermoset or thermoplastic polymer), and having an induction activateable adhesive on one or both outer surfaces. In another embodiment, the susceptor structure comprise a single foil layer which carries a reinforcing layer on one or both of its outer surfaces, and an induction activateable adhesive on one or both of its outer surfaces. The method of joining articles using these susceptor structures is also disclosed.

[0001] This application is based upon and claims priority from U.S.Provisional Patent Application No. 60/201,079, Malofsky, et al., filedApr. 28, 2000.

TECHNICAL FIELD

[0002] The use of induction heating in combination with adhesives tobond surfaces is known. Traditional foil susceptors used for suchoperations are difficult to handle without tearing where the susceptorsare soft, malleable, and thin. Handling difficulties are especiallyapparent where large amounts of materials are used, and especially largesheets or rolls of thin strips, such as for susceptor tapes. Aluminum isan excellent example of a susceptor material exhibiting suchcharacteristics. For aluminum foils in particular, these susceptors aregenerally two (2) mils or less in thickness for fast heating times withlightweight, air cooled, low powered (2 KW and below) tools, but can bethicker (greater than 2 mils) where longer heating times are acceptable.

[0003] While certain types of reinforced susceptors have previously beenused (see, for example, U.S. Pat. No. 5,717,191, Christensen, et al.,issued Feb. 10, 1998; U.S. Pat. No. 5,500,511, Hansen, et al., issuedMar. 19, 1996; U.S. Pat. No. 5,508,496, Hansen, et al., issued Apr. 16,1996; U.S. Pat. No. 5,705,795, Anderson, et al., issued Jan. 6, 1998;U.S. Pat. No. 5,705,796, Hansen, et al., issued Jan. 6, 1998; U.S. Pat.No. 5,723,849, Matsen, et al., issued Mar. 3, 1998; U.S. Pat. No.5,756,973, Kirkwood, et al., issued May 26, 1998; U.S. Pat. No.5,847,375, Matsen, et al., issued Dec. 8, 1998; U.S. Pat. No. 5,916,469,Scoles, et al., issued Jun. 29, 1999; U.S. Pat. No. 5,919,387, Buckley,et al., issued Jul. 6, 1999; and U.S. Pat. No. 5,919,413, Avila, issuedJul. 6, 1999), the described susceptors do not work well, if at all, forhigh speed bonding, especially for thin bond lines. These patentsgenerally teach susceptors having a thickness of about 2 mils orgreater, typically three (3) mils to ten (10) mils, that are coated onboth sides with adhesive, and optionally include a second layer oneither or both sides of a fiber reinforcement followed by another layerof continuous thermoplastic material. The final thickness of such aconstruction is at least 5 mils, more typically 10 mils or higher. Whileexcellent for high performance, dynamic load-tolerant bonding ofcomposite aerospace parts, the constructions are too thick, complicated,and expensive for use in all but specialized applications. Finally, thethickness of the susceptor, coupled with the thickness of the additionalreinforcement and plastic layers, makes heating very inefficient. Thisinefficiency is particularly noticeable where fast heating times (lessthan about 10 seconds, more preferably less than about 2 seconds, andmost preferably less than about 1 second) with lightweight, air cooled,low powered (2 KW and below) tools are desired. The operating conditionsof most interest are those necessary for foil or mesh-based RF heatingat frequencies less than about 40 mHz, more typically below about 1 mHz,most typically between about 1 kHz and about 500 kHz.

[0004] Reinforced thin metal sheets are also known for use as insulationmaterials (e.g., radiant heat barriers) and as sealing materials formedicine bottles. These materials are not used as susceptors for bondingoperations and, therefore, do not include an electromagneticallyactivateable adhesive layer.

[0005] It would be of particular interest if a new susceptor that wasthinner, more economical, and/or more efficient at heating the adhesivesystem or thermoplastics to be welded could be found. Such an innovationwould be useful in a wide range of bonding applications, not justspecialized ones, thereby allowing for improved bonding methods andfastener elimination in many industrial and consumer applications.However, such thin susceptors are extremely difficult to handle, tearingand folding easily. The following invention solves all of these problemswith a thinner structure, at lower cost, and at higher heatingefficiencies. The solution is especially effective for thin bond lines,and even more so for bonding where fast heating times (less than about10 seconds, more preferably less than about 2 seconds, and mostpreferably less than about 1 second) with lightweight, air cooled, lowpowered (2 KW and below) tools are desired.

SUMMARY OF THE INVENTION

[0006] The present invention relates to a susceptor article for use inelectromagnetically-induced fastening, comprising two foil layers eachof which has an inner and outer surface, and a reinforcing layersandwiched between said inner surfaces, said susceptor article carryingan induction activateable adhesive on at least one of its outersurfaces.

[0007] The invention also relates to a susceptor article which comprisesa foil layer having two outer surfaces, a reinforcing layer fastened toone or both of said outer surfaces and an induction activateableadhesive carried by one or both of said outer surfaces.

[0008] Finally, the invention relates to the method of fastening twotarget surfaces together wherein one of the susceptor articles,described above, is placed between and in contact with the two surfacesto be bonded, and is irradiated by electromagnetic energy therebyactivating the adhesive.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The novel susceptor structure of the present invention iscomposed, at the minimum, of at least one layer of anelectromagnetically activateable structure which produces heat via eddycurrent heating, hysteretic heating, or both, and which is fastened to areinforcing layer. The susceptor structure also includes an inductionactivateable adhesive on one or both sides. The layers are held togetherby conventional adhesive materials. Examples of the electromagneticallyactivateable structure include foils made from aluminum, steel, or othermetallic material, or non-metallic materials, such as specialized carbonor silicon. The term “structure,” as used herein, is meant to conveythat the materials used can be formed with a specific purpose eitherrelated or unrelated to this invention. For example, the susceptor maybe a thin sheet (foil), a thin sheet with perforations or holes, orderedor unordered, a thin mesh, and so on. The thickness of the susceptorstructure surface may optionally be coated either wholly or partiallywith surface treatments of varying kinds, including primers, adhesives,coupling agents, and so on. The susceptor is typically less than about 2mils, more preferably less than about 1 mil, and most preferably lessthan about 0.5 mil, thick.

[0010] The reinforcing layer can be made from any material that is notsubstantially electromagnetically activateable to produce heat, suchthat it provides improved strength to the new susceptor structure.Thermoplastic and thermoset polymer structures are typically utilized,optionally including some type of reinforcement that is isotropicallystrong. Examples of such an isotropic reinforcement are fibers,continuous or discontinuous, flakes, and the like, typically made fromcarbon, glass, olefin, aramid, boron, nylon, polyester, or cellulosicfibers, or combinations of these materials. The reinforcement may be ina continuous or discontinuous structure, and may be ordered (e.g., knit,cast, welded) or random (e.g., spun bonded). This layer is preferablyless than about 10 mils, more preferably less than about 2 mils, andmost preferably less than about 1 mil in thickness. Optional insulativematerials and/or layers may be added to restrict thermal losses to thereinforcing layer.

[0011] The reinforcing layer will generally be non-metallic and isselected such that it increases the tear strength of the susceptor (whenbonded to it) by at least a factor of about 2, preferably about 5, morepreferably about 10, most preferably about 25. The reinforcing layer canbe continuous or discontinuous, regular or irregular. Generally, thereinforcing layer will be in the form of a sheet, scrim or fibers (orcombination thereof), which can be fastened to the susceptor by anymethod know in the art. The most common method is through the use of anadhesive, as long as that adhesive is not softened by the application ofinduction energy (otherwise the susceptor may fall apart during thefastening process). Frequently used reinforcing materials includedorganic polymers, inorganic polymers, fibers, papers and combinationsthereof. Specific examples include olefinic polymers, polyesters,polyamides, polyurethanes, polyvinyls, and mixtures thereof. A preferredreinforcing material is polyethylene terphalate (PET). In someinstances, the adhesive used to hold the susceptor article together canalso act as the reinforcing layer.

[0012] The susceptor article may utilize a single susceptor sheet with areinforcing layer on one or both of its sides, and an inductionactivateable adhesive on one or both of its sides. Similarly, thesusceptor article may utilize a sandwich structure in which two (ormore) susceptor sheets sandwich one (or more) reinforcing layers. Insuch a structure, one or both of the outer sides of the susceptorarticle carries an induction activateable adhesive.

[0013] Induction activateable adhesives are well-known in the art.Specifically, these adhesives undergo a chemical or physical reaction(such as melting) upon the addition of electromagnetic energy whichcauses them to bond to an adjacent surface. Specific embodiments ofthese adhesives are shown in the examples of this application. Theseadhesives will be applied to one or both of the outer faces of thesusceptor article. They may be applied in a continuous or discontinuous,regular or irregular manner.

[0014] The article may consist of a single susceptor/reinforcing layer“sandwich” or may consist of multiple sandwich layers. The outersurfaces of the susceptor may carry a heat-activateable (inductionactivateable) adhesive to effect bonding to a target surface. One of theouter surfaces of the susceptor may have attached to it a material(e.g., decorative wood, wallpaper, fabric) which can be affixed to thetarget surface using the device of the present invention.

[0015] A key aspect of the present invention is that it provides thinnersusceptors (e.g., about 5 mils or less, preferably about 3 mils or less)that can be bound with only one major reinforcement layer whilesimultaneously providing for direct contact of the adhesive system orstructure or the weldable surface with the electromagnetically heatablesusceptor structure. No prior art teaches or suggests such a structure.In fact, it is only in the packaging and insulating industries that onefinds examples of somewhat similar structures for moisture barriers,reflective heat or cooling insulation, and cap-sealing materials.

[0016] The overall structures may be flat, textured, perforated, or anycombination thereof. Either a portion or all of the susceptor structurecan be reinforced. The reinforcement can vary in strength from onesection to another. Changes are meant to facilitate handling, assemblyof objects, or their disassembly. The structures may be utilized assheets, discs, strips and so on, and may be stored as rolls, coils, orflat stacks.

[0017] In the method aspect of the present invention, the susceptorarticle of the present invention (particularly one having inductionactivateable adhesive on both of its outer surfaces) is placed betweenand in contact with two surfaces to be joined (i.e., one outer side ofthe susceptor article is in contact with each of the surfaces to bejoined). The area to be fastened (i.e., the susceptor article) is thenirradiated with electromagnetic energy, preferably having a frequencybetween 1 and about 1 mHz, most preferably from a hand-held tool, forfrom about 0.01 to about 10 seconds. The electromagnetic energy may beapplied continuously or in pulses. This energy interacts with thesusceptor to form heat energy which activates the adhesive, bonding thesurfaces to be joined.

EXAMPLES

[0018] Susceptor Layer 1: 0.25 mil aluminum foil, perforated or un-perforated, textured or untextured Optional Surface Adhesion promotercoating Treatments: Adhesion promoter primer coating Surface treatmentto either or both sides of the aluminum, i.e., anodization, chemicaletching Optional Adhesive To bond foil (layer 1) to reinforcement layer,Layer 1 i.e., a polyamide, polyester, or ethylene vinyl acetate-basedfilm formulation. Reinforcement Polyester, nylon, polyamide,polyethylene, Layer: polybutylene, urethane , or other adhesive orpolymeric cast resins, cured coatings, or films, 0.1 to 1.5 mils thick,perforated or un- perforated, textured or untextured (see below)Optional Reinforcement Continuous glass or other structural fibers orAdditions: fiber bundles, positioned in an isotropic network spaced 1-2cm apart in a square array within or laminated to the polymer film. Athin foam film 1-50 mils thick between two layers of polymeric film asan insulator to obviate thermal losses or to provide certain degrees ofmechanical performance, i.e., cushioning or expansion/contraction loaddissipation. Optional Adhesive To bond foil (layer 2) to reinforcementlayer, Layer 2 i.e., a polyamide, polyester, or ethylene vinyl acetatebased film formulation. Susceptor Layer 2: 0.25 mil aluminum foil,perforated or un- perforated, textured or untextured Optional SurfaceAdhesion Promoter coating Treatments: Adhesion Promoter Primer coatingSurface treatment to either or both sides of the aluminum, i.e.,anodization, chemical etching Laminating Process: The susceptor layersare laminated together using any number of adhesive systems that mayconsist of water-based, solvent-borne or other liquid polymer systems.Depending upon the system employed, drying or curing mechanisms may berequired. These may include UV curing systems, IR or heat ovens. Theadhesive layer thickness can be anywhere from a fraction of a mil (0.1mil) to several mils in thickness. Laminating processes may includeknife over roll, curtain coater, or in some cases a co-extrusion processcan be employed using thermoplastic layers as the adhesive between thesusceptors.

What is claimed is:
 1. A susceptor article for use inelectromagnetically-induced fastening, comprising two foil layers eachof which has an inner and outer surface, and a reinforcing layer whichis sandwiched between said inner surfaces, said susceptor carrying aninduction activateable adhesive on at least one of its outer surfaces.2. The susceptor article according to claim 1 where the foil layers arefastened to the reinforcing layer.
 3. The susceptor article according toclaim 2 wherein the thickness of each foil layer is no greater thanabout 2 mils.
 4. The susceptor article according to claim 3 wherein thefoil layers are made from aluminum.
 5. The susceptor article accordingto claim 4 wherein the reinforcing layer is selected from sheets,scrims, fibers and mixtures thereof.
 6. The susceptor article accordingto claim 5 wherein the reinforcing layer is selected from organicpolymers, inorganic polymers, fibers, papers and mixtures thereof. 7.The susceptor article according to claim 6 wherein the reinforcing layeris selected from olefinic polymers, polyesters, polyamides,polyurethanes, polyvinyls and mixtures thereof.
 8. The susceptor articleaccording to claim 7 wherein the reinforcing layer comprisespolyethylene terphthalate.
 9. The susceptor article according to claim 6wherein the thickness of each foil layer is no greater than about 0.5mil.
 10. The susceptor article according to claim 3 having a totalthickness of no greater than about 5 mils.
 11. The susceptor articleaccording to claim 6 which carries an induction activateable adhesive onboth of its outer surfaces.
 12. The susceptor article according to claim6 which carries an induction activateable adhesive on one of its outersurfaces and carries a substrate to be fastened to a target surface onits other outer surface.
 13. A susceptor article for use inelectromagnetically-induced fastening, comprising a foil layer havingtwo outer surfaces, a reinforcing layer fastened to at least one of saidouter surfaces, and an induction activateable adhesive carried by atleast one of said outer surfaces.
 14. The susceptor article according toclaim 13 wherein an induction activateable adhesive is carried by bothof said outer surfaces.
 15. The susceptor article according to claim 13wherein the thickness of the foil layer is no greater than about 2 mils.16. The susceptor article according to claim 15 where the foil layer ismade from aluminum.
 17. The susceptor article according to claim 16wherein the reinforcing layer is selected from sheets, scrims, fibersand mixtures thereof.
 18. The susceptor article according to claim 17wherein the reinforcing layer is selected from organic polymers,inorganic polymers, fibers, papers and mixtures thereof.
 19. Thesusceptor article according to claim 18 wherein the reinforcing layer isselected from olefinic polymers, polyesters, polyamides, polyurethanes,polyvinyls and mixtures thereof.
 20. The susceptor article according toclaim 19 wherein the reinforcing layer comprises polyethyleneterphthalate.
 21. The susceptor article according to claim 18 whereinthe thickness of the foil layer is no greater than about 0.5 mil. 22.The susceptor article according to claim 13 having a total thickness ofno greater than about 5 mils.
 23. The susceptor article according toclaim 13 having a reinforcing layer fastened to both of its outersurfaces.
 24. The susceptor article according to claim 23 wherein aninduction activateable adhesive is carried on both of its outersurfaces.
 25. The susceptor article according to claim 23 wherein thethickness of the foil is no greater than about 2 mils.
 26. The susceptorarticle according to claim 25 where the foil layer is made fromaluminum.
 27. The susceptor article according to claim 26 wherein thereinforcing layer is selected from sheets, scrims, fibers and mixturesthereof.
 28. The susceptor article according to claim 27 wherein thereinforcing layer is selected from organic polymers, inorganic polymers,fibers, papers and mixtures thereof.
 29. The susceptor article accordingto claim 28 wherein the reinforcing layer is selected from olefinicpolymers, polyesters, polyamides, polyurethanes, polyvinyls and mixturesthereof.
 30. The susceptor article according to claim 29 wherein thereinforcing layer comprises polyethylene terphthalate.
 31. The susceptorarticle according to claim 28 wherein the thickness of the foil layer isno greater than about 0.5 mil.
 32. The susceptor article according toclaim 28 having a total thickness of no greater than about 5 mils. 33.The method of fastening two target surfaces comprising placing thesusceptor article of claim 11 between said target surfaces, andirradiating said susceptor with electromagnetic energy having afrequency of from about 1 kHz to about 1 mHz for from about 0.01 toabout 10 seconds.
 34. The method of claim 33 wherein the electromagneticenergy is applied from a hand-held tool.
 35. The method of fastening twotarget surfaces comprising placing the susceptor article of claim 14between said target surfaces, and irradiating said susceptor withelectromagnetic energy having a frequency of from about 1 kHz to about 1mHz for from about 0.01 to about 10 seconds.
 36. The method of claim 35wherein the electromagnetic energy is applied from a hand-held tool. 37.The method of fastening two target surfaces comprising placing thesusceptor article of claim 24 between said target surfaces, andirradiating said susceptor with electromagnetic energy having afrequency of from about 1 kHz to about 1 mHz for from about 0.01 toabout 10 seconds.
 38. The method of claim 37 wherein the electromagneticenergy is applied from a hand-held tool.